Use of CodeIgnitor with a sub-application

[eluser]Durkin[/eluser]
At the moment I have a basic chat application built with no framework that is very simple to use, with only core features. I am working on a new version, and will be basing it around the Code Igniter framework. My question is, should the chat application be added on to the whole application, or should I rewrite with Code Igniter. As it makes use of AJAX calls frequently to update etc, my real concern is if using a framework (which really isn't needed) for a large quantity of calls will increase the overhead. While I assume that it will increase the overhead, it will be easier to maintain.

As I have no experience with Code Igniter, I've just had a quick look through the documentation, do you mix Code Igniter files and have a sub folder with just normal php, or is this a maintenance nightmare. As it is a chat application, my main thoughts are for speed, however I have no experience as to whether Code Igniter will create a large overhead for requests that don't need the full functionality. Any thoughts?

[eluser]Phil Sturgeon[/eluser]
Will you be including the code for this chat script into the CodeIgniter code or is it just running separately?

[eluser]Durkin[/eluser]
That's what I am trying to work out. As I see it, converting the chat script to work with Code Igniter will make long term maintenance easier simply because it is consistent with the rest of the site, however I assume performance will drop due to the overhead of having a framework. I am just trying to gather views as to whether the maintenance problem will be bad or the overhead is horrible etc. as I haven't used Code Igniter before.

I have only created a rough prototype of the chat program, so rewriting it to be used with Code Igniter isn't a problem.

[eluser]Phil Sturgeon[/eluser]
If it is not integrated with CodeIgniter in any way, then just having it sat next to (or within) the CodeIgniter directory will not be an issue at all.

If you add includes to the chat script within your CodeIgniter script, then yes, it will cause an overhead as you are including extra code.

Rebuilding it in CodeIgniter would be cool, but really wouldnt make any difference to overhead. The CodeIgniter version would of course be slightly slower than native PHP. You would be better leaving it as pure PHP as AJAX will run faster outside of the framework.